历史上最早的成文法典是古代西亚乌尔第三王朝创始者乌尔纳姆颁布的。它适应奴隶制的发展，主要用来保护奴隶占有和私有制经济，镇压奴隶和贫民的反抗。这部法典大部损坏，只剩残片。乌尔第三王朝（约公元前2113~前2006年）创始人乌尔纳姆（约公元前2113~前2096年在位）建立了强大的中央集权制度，总揽全国大权，统一两河流域的法律，适应奴隶制的发展和奴隶主镇压奴隶反抗的需要，缓和自由民内部的矛盾，他下令用苏美尔文（楔形文字）写成了一部适用于乌尔全境的法典，这便是《乌尔纳姆法典》。
法典包括序言和正文29条（传下来的只有23条）两大部分，没有结语，主要涉及政治、宗教和法律等方面。序言宣称，是神授予乌尔纳姆统治权力，乌尔纳姆在人世间的行为是按照神意，确立「正义」和「社会秩序」，并列举了他在保护贫弱、抑制豪强等方面所采取的措施。
现已发现的最早抄本大约是巴比伦时代的，但大部分已毁损，仅存几条残片。从破损较严重的法典残片看，法典的主要内容是对奴隶制度、婚姻、家庭、继承、刑罚等方面的规定。如：第一次离婚支付1米纳白银，而第二次离婚应当支付1/2米纳白银，通奸者将被处死；强暴自己的女奴者将被课以5西克尔罚金；作伪证将被处以罚款；斗殴中打折骨头需支付1米纳白银，损伤脚需支付10西克尔；外国人的土地被淹没，每0.3公顷土地将给予3古尔（约900公升大麦）补偿；将逃亡奴隶捉回的奴隶主要给捕捉者适当的报酬；伤害他人的身世要处以酷刑并罚款；禁止行巫术；破坏他人耕地者要支付食物赔偿；女奴对女主人不敬则予体罚。妇女在家庭中地位低下，如犯通奸罪则处死等等。这些条文充分表明了当时立法已采用罚金赔款等方式逐步取代同态复仇。
从现在仅存的二十多条残篇来看，涉及女奴的有五条，她们时常遭受强暴、买卖和殴打；有两条涉及寡妇，她们的社会地位较之女奴较好——法典序言提到不允许有势力的人支配寡妇，正文又提到遗弃寡妇的男人应赔偿一定数额的白银；法典也涉及普通妇女，她们的社会地位比女奴和妇女高，但较普通男子卑下。尽管法典中仍残存着让河神澄清妖术罪和妻子被控通奸罪的规定，但有关身体伤害的处罚规定比原始的处罚有了很大的进步。
《乌尔纳姆法典》无论在内容上或形式上，都有创新之处，在西亚地区占有重要的地位，对后来两河流域各国制定的法典影响颇大。
序言
The prologue, typical of Mesopotamian law codes, invokes the deities for Ur-Nammu's kingship and decrees "equity in the land".
"…After Anand Enlilhad turned over the Kingship of Ur to Nanna, at that time did Ur-Nammu, son born of Ninsun, for his beloved mother who bore him, in accordance with his principles of equity and truth... Then did Ur-Nammu the mighty warrior, king of Ur, king of Sumer and Akkad, by the might of Nanna, lord of the city, and in accordance with the true word of Utu, establish equity in the land; he banished malediction, violence and strife, and set the monthly Temple expenses at 90 gur of barley, 30 sheep, and 30 sila of butter. He fashioned the bronze sila-measure, standardized the one-minaweight, and standardized the stone weight of a shekelof silver in relation to one mina... The orphan was not delivered up to the rich man; the widow was not delivered up to the mighty man; the man of one shekel was not delivered up to the man of one mina."
正文
1. If a man commits a murder, that man must be killed.
2. If a man commits a robbery, he will be killed.
3. If a man commits a kidnapping, he is to be imprisoned and pay 15 shekels of silver.
4. If a slave marries a slave, and that slave is set free, he does not leave the household.
5. If a slave marries a native (i.e. free) person, he/she is to hand the firstborn son over to his owner.
6. If a man violates the right of another and deflowers the virgin wife of a young man, they shall kill that male.
7. If the wife of a man followed after another man and he slept with her, they shall slay that woman, but that male shall be set free. (§4 in some translations)
8. If a man proceeded by force, and deflowered the virgin slavewoman of another man, that man must pay five shekels of silver. (5)
9. If a man divorces his first-time wife, he shall pay her one mina of silver. (6)
10. If it is a (former) widow whom he divorces, he shall pay her half a mina of silver. (7)
11. If the man had slept with the widow without there having been any marriage contract, he need not pay any silver. (8)
13. If a man is accused of sorcery he must undergo ordeal by water; if he is proven innocent, his accuser must pay 3 shekels. (10)
14. If a man accused the wife of a man of adultery, and the river ordeal proved her innocent, then the man who had accused her must pay one-third of a mina of silver. (11)
15. If a prospective son-in-law enters the house of his prospective father-in-law, but his father-in-law later gives his daughter to another man, the father-in-law shall return to the rejected son-in-law twofold the amount of bridal presents he had brought. (12)
17. If a slave escapes from the city limits, and someone returns him, the owner shall pay two shekels to the one who returned him. (14)
18. If a man knocks out the eye of another man, he shall weigh out ½ a mina of silver. (15)
19. If a man has cut off another man’s foot, he is to pay ten shekels. (16)
20. If a man, in the course of a scuffle, smashed the limb of another man with a club, he shall pay one mina of silver. (17)
21. If someone severed the nose of another man with a copper knife, he must pay two-thirds of a mina of silver. (18)
22. If a man knocks out a tooth of another man, he shall pay two shekels of silver. (19)
24. [...] If he does not have a slave, he is to pay 10 shekels of silver. If he does not have silver, he is to give another thing that belongs to him. (21)
25. If a man’s slave-woman, comparing herself to her mistress, speaks insolently to her, her mouth shall be scoured with 1 quart of salt. (22)
28. If a man appeared as a witness, and was shown to be a perjurer, he must pay fifteen shekels of silver. (25)
29. If a man appears as a witness, but withdraws his oath, he must make payment, to the extent of the value in litigation of the case. (26)
30. If a man stealthily cultivates the field of another man and he raises a complaint, this is however to be rejected, and this man will lose his expenses. (27)
31. If a man flooded the field of a man with water, he shall measure out three kur of barley per iku of field. (28)
32. If a man had let an arable field to a(nother) man for cultivation, but he did not cultivate it, turning it into wasteland, he shall measure out three kur of barley per iku of field. (29)
乌尔纳姆（Ur-Nammu）约公元前2113年－公元前2096年在位阿卡德王国灭亡后，蛮族库提人统治苏美尔地区，虽然其间有些苏美尔城邦保持着相对的独立和繁荣。公元前2120年，渔夫出身的乌鲁克人乌图赫加尔起兵自立为乌鲁克王，并且打败了库提人，俘获了库提人的末代国王梯里根（Tiriga），乌图赫加尔占领乌尔后任命乌尔纳姆治理乌尔。乌图赫加尔与乌尔纳姆的关系现在仍是史学界研究的课题，一说乌尔纳姆是乌图赫加尔的弟弟，另一说乌尔纳姆则是乌图赫加尔的女婿。但可能在乌图赫加尔尚在世时，乌尔纳姆就已经与他反目为仇，不臣服于他了。约公元前2112年，乌图赫加尔死于一场意外（或者可能是阴谋）。此后乌尔纳姆南征北战，继阿卡德王国以后，统一整个美索不达米亚，建立起了强大的中央集权制王朝。（另一强大的苏美城邦拉格什于约公元前2110年被征服）乌尔纳姆留给后人一部《乌尔纳姆法典》，今天考古所得的只是这部法典的一小部分。
《乌尔纳姆法典》是部成熟的法律，苏美尔文明的法制体系已经经历了很长时间的发展。虽然如此，《乌尔纳姆法典》但仍然可视为人类文明史上现存的最早的成文法。
